1. Field of the Invention
The present invention relates to a manufacturing method for a semiconductor unit in which a package for mounting a semiconductor device is made of a resin.
2. Description of the Related Art
In a semiconductor unit requiring optical characteristics such as a CCD linear sensor, CCD area sensor, light emitting element and EPROM, a semiconductor device is contained in a translucent package to be protected from external disturbance.
In the case of a hollow ceramics package, a recessed hollow portion is provided in a base member made of ceramics at its approximately central portion, and a semiconductor device is mounted in the recessed hollow portion and is subjected to wiring by means of a wire bonding. After that, in such a state, a seal glass is bonded on the upper surface of the base member through a B stage sealer or A stage sealer for sealing the semiconductor device and the bonding wire.
In terms of reduction in cost, there has been proposed a semiconductor unit 10' as shown in FIG. 4A, which includes a hollow package having a base member 5 made of an epoxy resin. The semiconductor unit 10' including such a hollow package is manufactured as follows. A lead frame 3 is held between upper and lower molds, and in such a state, a cavity formed between the upper and lower molds is filled with an epoxy resin by transfer molding, to mold a base member 5 having a recessed portion 51 at its approximately central portion and a frame portion 6 on the base member 5. Next, after burring by blasting of beads or the like, a film of a nickel-gold alloy or the like is formed on an exposed outer lead portion and inner lead portion by electroplating.
A semiconductor device 7 is mounted in the recessed portion 51, and is connected to the lead frame 3 by means of a wire bonding 8. A seal glass 92 is then bonded to the upper surface of the frame portion 6 on the base member 5 through a B stage sealer or A sealer stage.
In this case, the epoxy resin used for molding the base member 5 of the hollow package is added with an additive for reducing a moisture absorption property of the epoxy resin. Alternatively, as shown in a sectional view of FIG. 4B, a semiconductor unit 10" is manufactured in a method wherein a pad portion 33 of the lead frame 3 subjected to a dipless process is buried in the base member 5 for preventing the permeation of moisture in the recessed portion 51.
In the above-described semiconductor unit including a hollow ceramics package, however, the processes of manufacturing a base member made of ceramics are complicated, so that it becomes very difficult to shorten a manufacturing time and to reduce a manufacturing cost.
The above-described semiconductor unit including a base member formed of an epoxy resin by transfer molding is advantageous in shortening a manufacturing time as compared with the hollow ceramics package; however, it is disadvantageous in that the camber of the base member after being molded (after hardening of the epoxy resin) becomes larger, thereby making it difficult to mount a semiconductor device at an accurate position and to air-tightly seal it by bonding a seal glass on the unit.
In the hollow package including the epoxy resin made base member, the burring is also required, and a cleaning operation for the molds becomes complicated. This reduces productivity, thereby making it difficult to reduce the manufacturing cost.
In particular, for a semiconductor unit in which a long-size semiconductor device must be mounted in a base member, such as a CCD linear sensor, the semiconductor device is difficult to mount at an accurate position because of the camber of the base member, thus exerting an adverse effect on the optical characteristics of the unit.
In the hollow package having the epoxy resin made base member, moreover, there is a fear that a semiconductor device causes malfunction due to radiation from impurities contained in the base member. To prevent this inconvenience, a refining cost for refining a material for the base member is increased, failing to reduce the manufacturing cost.